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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Hill cipher ： ウィキペディア英語版 Hill cipher In classical cryptography, the Hill cipher is a polygraphic substitution cipher based on linear algebra. Invented by Lester S. Hill in 1929, it was the first polygraphic cipher in which it was practical (though barely) to operate on more than three symbols at once. The following discussion assumes an elementary knowledge of matrices. ==Operation== Each letter is represented by a number modulo 26. (Often the simple scheme A = 0, B = 1, ..., Z = 25 is used, but this is not an essential feature of the cipher.) To encrypt a message, each block of ''n'' letters (considered as an ''n''-component vector) is multiplied by an invertible ''n'' × ''n'' matrix, again modulus 26. To decrypt the message, each block is multiplied by the inverse of the matrix used for encryption. The matrix used for encryption is the cipher key, and it should be chosen randomly from the set of invertible ''n'' × ''n'' matrices (modulo 26). The cipher can, of course, be adapted to an alphabet with any number of letters; all arithmetic just needs to be done modulo the number of letters instead of modulo 26. Consider the message 'ACT', and the key below (or GYBNQKURP in letters): : Since 'A' is 0, 'C' is 2 and 'T' is 19, the message is the vector: :$\backslash begin\; 0\; \backslash \backslash \; 2\; \backslash \backslash \; 19\; \backslash end$ Thus the enciphered vector is given by: : which corresponds to a ciphertext of 'POH'. Now, suppose that our message is instead 'CAT', or: :$\backslash begin\; 2\; \backslash \backslash \; 0\; \backslash \backslash \; 19\; \backslash end$ This time, the enciphered vector is given by: : which corresponds to a ciphertext of 'FIN'. Every letter has changed. The Hill cipher has achieved Shannon's diffusion, and an n-dimensional Hill cipher can diffuse fully across n symbols at once. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hill cipher」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.